The World Health Organization defines the presence of osteoporosis in humans in terms of low bone mineral density BMD. Individuals whose BMD is less than 2.5 standard deviations below the mean of young normals of their sex in respect of peak bone mass, are considered to have osteoporosis. Individuals whose BMD is less than 1.0 standard deviations below peak bone mass of their sex, are considered to have osteopenia. Osteoporosis results in a higher probability of fracturing bones. It is well known that women have a higher prevalence of osteoporosis and fractures compared to males, and that there is an increased prevalence of osteoporosis and associated increased incidence of fractures after the menopause. Low impact injuries can result in osteoporotic fractures, or so called “fragility fractures”. BMD is a good predictor of the probability of developing an osteoporotic fracture, but it is generally agreed that the information that BMD provides is incomplete, as it does examine the quality of bone. BMD is usually measured by a standard radiographic technique, dual energy X-ray absorptiometry (DXA). This is the most standardized technique currently used and has become much more readily available in the Western world for human studies. However, in most of the world DXA is not readily available or is too expensive for routine use. There are many other ways that the presence of osteoporosis can be detected or suspected in humans and other mammals. DXA technology, with suitably adapted software, can be used to reliably assess BMD in animal studies.
Fractures can occur also after high impact, as a result of significant trauma, in individuals with normal bones or osteoporotic or osteopenic bones. The healing of high impact fractures depends on stimulation of new bone formation. Local osteoporosis can occur as a result of immobilization during the treatment of the fracture.
Although BMD is a reasonably good predictor of the risk of fracture in sites such as the hip or spine it is becoming increasingly recognized that there are a number of limitations to the usefulness of BMD measurements. One of the reasons is that DXA technology does not assess bone quality, which depends to a large extent on the micro-architecture of bone. Most drugs used in osteoporosis, such as the bi-phosphonates, increase BMD but do not improve the micro-architecture or the connectivity of bone. Parathyroid hormone administration results in an improvement of trabecular architecture. Glucosamine-based synthetic compounds are not known to improve BMD or bone microarchitecture.